Method of electric heating



June 12, 1928.

' 1,673,226 B. o. BUSHELL ET' AL METHOD OF ELECTRIC HEATING Filed Aug. 7, 1926 .277 wen/or v 3 D \Bus/zo// JCT TE w/n and 6. 42. Era/7a g mama June 12,1928.

UNITED STATES.

PATENT OFFICE.

BENJAMIN DANIEL .BUSHELL, OI SPRINGS, SYDNEY EDWARD TRACKER EWING, OF

J'OHANNESBUBG, 'VAAL, SOUTH AFRICA.

AND ERNEST HENRY IJOKINICUS BBUNNER, OI SPRINGS, TRANS- METHOD OF ELECTRIC HEATING.

Application filed August 7. 1928, Serial Io. 127,947, and in the Union of South Airica lay 8, me.

The operations of mining, tunneling and the like necessitate the useof large numbers of steel tools, such as rock drill tools, coalcutter tools, picks and the like having hardened cutting or striking ends. As these become blunted they have to be re-sharpened I by forgin and re-hardened after forging.

I It is not easible to heat the tools for these purposes in the enclosed space of a mine or tunnel by means of the usual fuel-burning furnaces since the latter vitiate the air and give ofi large quantities of wasted heat; and

1t is accordingly the practice to convey the blunted tools to the surface and to return them underground after they have been sharpened and hardened. This involves considerable expense for transportation and also unprofitable outlay for a much greater number of tools than are at any time in use.

The present invention provides an electrical method and apparatus for heating such tools which produce heat only in the limited portion of the tool which requires to be heated, thus minimizing heating of the atmosphere. Since also the apparatus 'ves of no injurious fumes, it can be use underground for forging and hardening tools near to their place of use, thus enabhng the expense of transportation f tools to be materiso ally reduced and a conslderable saving to be made in the cost of the tool eiuipment.

Ap t e invention is paratus according to illustrated in the accompanying drawing in I which a as Fig. I is a general pers ective view,

Fig. 11 is a view, to a di erent scale, showing the end of a drill tool positioned for heat- Fig. III 1s a plan of Fig. II,

'40 Fig. IV shows modified 2 indi tes a bench on which are mounted electrode clamps 3, 4. The clamp 3 is fixed to, but insulated from the bench. The ch31 4'is mounted on a guide 5 to slide tow and from the clamp 3 being traversed by such means as the feed screw 6 which enges the renewable nut 7 and is actuated the capstan wheel 8. The latter is convenientl tpositioned for actuation by one so hand 0 e operator while other hand is em loyedwith the tool 9wlnch is to be hea 10, 11 indicate an adjustable transformer,

the low-voltage winding 11 of which is connected to the electrode clamps 3-, 4, by leads 12, 13 respectively, the lead 13 being flexible to allow the necessary movement of clamp 4.

An important feature of the apparatus is the means enabling the operator to switch the current on and off rapidl and frequently without interference wit the necessary manipulation of the work and the ma- I chine. Accordingly there is. provided in the high-voltage circuit a switch 14 opened by a spring 15 and closed by a pedal 16 con-. vemently positioned for actuation by the operator when he is standing in the position to hold the workwith one hand and to operate the capstan wheel 8 with the other hand.

The electrode clamps 3, 4, are hollow and are cooled by water clrculated through them by pipes 17, 18.

The opposing faces of the electrode clamps are providedwith detachable jaws 19. The contacting faces of the jaws and clamps are machined to make good electrical contact and are secured in close mechanical contact by the clips 20.

The body to be heated is clamped at its sides between the inner faces of the jaws 19; and said inner faces are sha d to the general form or profile of the b0 y so as to make reasonably good electrical contact therewith. The drawin illustrate the heating, for forging, of t e flared cutting end of a cruciform rcussive rock drill tool 9. The jaw faces or this purpose comprise plane areas 21 slo ed to one another correspondingly with t e profile of the drill wings 22 and curved shoulders 23 fitting the neck 24 of the drill.

The tool is supported in a horizontal position and perpendlcularl to the direction of movement 0 the jaws y an insulated rest 25 near to the clamps and a portable rest 26 podtioned at a suitable distance from the bench according to the length of the drill.

In operation it is desirable to pickle the end of the drill in order to remove from its surface non-conducting material such as scale. The pickled dnll is placed on the rests 25, 26 m the proper position for its flared end22tobeenga'ged by the sloped surfaces 21 of the clamp jaws; and the capstan 1 5 wheelBisactuatedtocausetheendtobo low-voltage current to flow between the electrodes and transversely through the drill end. A heavy current of say 17,000 amperes is employed, resulting in rapidheatin'g of v the drill end.

Owing to the irregular cross sectional form of the drill end, heating takes place most rapidly at localized points, for example, at

the neck 24 and at the edges of the wings 22. As soon as this uneven heating becomes pronounced the current is switched off by releasing the pedal 16;- whereupon heat quickly flows from the more highly heated to the less heated zones of the end. After a short interval-current is again switched on and once more switched off when the ir regular heating again becomes pronounced; this bein re eated several times until the whole en 1s ii to the desired temperature. The pedal 16 is thereupon finally released, the capstan wheel 8 is operated to retract the clamp 4, and the drill is removed.

With the controls conveniently arranged as shown so that while holding the drill in one hand, the operator can turn the'wheel 8 with his other hand and operate the pedal 16 with his foot; using an appropriate eavy current; and switching on and off three or four times in each heat, one man can readily heat numbers of drill ends to forging temperature at the rate of about four per minute.

As the jaws 19 become worn and out of shape by repeated closin onto the drill, they may be adjusted to brin fresh parts of their surfaces into use by loosening the clips 20 and adjusting the jaws vertically. Fig. I shows a worn part 21 thus raised out of clam ing position.

For different classes'of work other'aws differing in the form of their inner. aces are employed. Those illustrated being intended for heating a drill end for forging, are shaped as previously described to engage the entlre flared end of'the drill from the tip to the neck. For hardening the forged dnlls, jaws shorter in the direction of the eated substantially uniformly axis of the drill may be used or the drill may be drawn back, with the object in both cases of confining the heating current more to the point of the drill. For other tools, jaws of appropriate shape areused; Fig. IV illustrating jaws for heating the tips of a pick head.

It will be'seen that by reason of the elecbody which is of generally elongated form and which varies in cross section at difi'erent parts of its length, the said method consistmg in passing heating electric current transversely across a plurality of difl'eient cross sections of said body and repeatedl ,lnterrupting the heating current at sue intervals and for such periods as on the one hand to avoid overheating of the cross sections more readily heated by the heating currents and on the other hand to allow heat to be conducted from such cross sections to cross sections which the current tends to heat less rapidly, and thereby promote thev uniform heatin of the body.

2. T e method of heating the flared end of a percussive rock drilling tool accordlng to claim.1, in which the heating current 1s passed transversely across said end at substantially all its cross sections, and in whlch the current is so interrupted that the free extremity of said end becomes heated to a tem erature not less than the remainder of sai end.

In testimony whereof we aflix our signatures.

BENJAMIN DANIEL BUSHELL SYDNEY EDWARD THACKER EWING. ERNEST HENRY DOHINICUS BRUNNER. 

